A heat-absorbing glass plate is required to have a solar transmittance sufficiently lower than the visible light transmittance. That is, it is required to have a high ratio Tv/Te of the visible light transmittance (by illuminant A, 2° visual field) as defined in JIS R3106 (1998) (hereinafter sometimes referred to as Tv) calculated as 4 mm thickness of the glass plate to the solar transmittance as defined in JIS R3106 (1998) (hereinafter sometimes referred to as Te) calculated as 4 mm thickness of the glass plate.
Further, the heat-absorbing glass plate may sometimes be required to have low Tv in order that the interior is hardly seen through the glass plate from the outside to secure privacy.
Further, the heat-absorbing glass plate is required to provide a substantially achromatic (gray) transmitted light, that is, to have a low excitation purity Pe as defined in JIS Z8701 (1999) (hereinafter sometimes referred to as Pe), in order that an object or a scene can be seen in the actual colors when observed through the glass plate.
As a heat-absorbing glass plate having a low Pe, for example, the following glass plate has been proposed.
(1) A heat-absorbing glass plate (Patent Document 1) containing, as represented by mass % based on the following components:
SiO2: 66 to 75%,
Na2O: 10 to 20%,
CaO: 5 to 15%,
MgO: 0 to 5%,
Al2O3: 0 to 5%,
K2O: 0 to 5%,
total iron as calculated as Fe2O3: 0.30 to 0.70%,
divalent iron as calculated as FeO: at most 0.21%,
CoO: 3 to 35 ppm, and
Se: 1 to 15 ppm,
wherein the luminous transmittance is at least 60% in 3.9 mm thickness, the dominant wavelength is from 480 to 559 nm, and the excitation purity is at most 8% in 3.9 mm thickness.
(2) A heat-absorbing glass plate (Patent Document 1) containing, as represented by mass % based on the following components:
SiO2: 66 to 75%,
Na2O: 10 to 20%,
CaO: 5 to 15%,
MgO: 0 to 5%,
Al2O3: 0 to 5%,
K2O: 0 to 5%,
total iron as calculated as Fe2O3: 0.17 to 0.65%,
divalent iron as calculated as FeO: at most 0.18%,
CoO: 15 to 55 ppm,
Se: 0 to 5 ppm, and
NiO: 50 to 350 ppm,
wherein the luminous transmittance is at least 60% in 3.9 mm thickness, the dominant wavelength is from 480 to 580 nm, and the excitation purity is at most 8% in 3.9 mm thickness.
(3) A heat-absorbing glass plate (Patent Document 2) containing, as represented by mass % based on oxides:
SiO2: 66 to 75%,
Na2O: 10 to 20%,
CaO: 5 to 15%,
MgO: 0 to 5%,
Al2O3: 0 to 5%,
K2O: 0 to 5%,
total iron as calculated as Fe2O3: 0.40 to 1.0%,
CoO: 4 to 20 ppm, and
Cr2O3: 0 tO 100 ppm,
wherein the mass ratio (FeO/t-Fe2O3) of divalent iron as calculated as FeO to total iron as calculated as Fe2O3 is from 0.35 to 0.50, the luminous transmittance is at least 65% in 3.9 mm thickness, the dominant wavelength is from 485 to 489 nm, the excitation purity is from 3 to 18%, the total solar energy transmittance is at most 55% in 3.9 mm thickness, the total solar ultraviolet transmittance is at most 60% in 3.9 mm thickness, and the total solar infrared transmittance is at most 35% in 3.9 mm thickness.
(4) A heat-absorbing glass plate (Patent Document 3) containing, as represented by mass % based on the following components:
SiO2: 65 to 75%,
Na2O: 10 to 20%,
CaO: 5 to 15%,
MgO: 0 to 5%,
Al2O3: 0 to 5%,
K2O: 0 to 5%,
total iron as calculated as Fe2O3: 0.30 to 0.75%,
CoO: 0 to 15 ppm, and
Se: 1 to 15 ppm,
wherein the mass ratio (FeO/t-Fe2O3) of divalent iron as calculated as FeO to total iron as calculated as Fe2O3 is from 0.26 to 0.675, the luminous transmittance is at least 65% in 3.9 mm thickness, the total solar energy transmission (TSET) is at most 65%, the standard transmitted color shift is less than 6, and the excitation purity is less than 8%.